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Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

We assessed satellite‐retrieved marine aerosol in the western Antarctic Peninsula (WAP) across a 12‐year period from coarse‐mode aerosol optical depth (AODC), often used as a proxy for sea spray aerosol (SSA), and marine aerosol optical depth (MAOD), a newly developed proxy for tropospheric marine aerosol. Across open ocean to coastal regions, daily fluctuations in nighttime and daytime winds, respectively, drove increasing MAOD and AODC. MAOD depicted strong correlations with wind speed across open ocean and weak correlations in coastal regions. In the open ocean, AODCexhibited a very weak significant correlation to wind speed and a weak significant correlation to sea surface temperature (SST). We thus observed that warmer SST enhanced the production of SSA, supporting prior studies. This is the first study to assess patterns of AODCin the WAP. In contrast to the tropical Pacific, seasonal patterns showed that biological activity likely contributed toward MAOD and AODCmagnitudes. The production of marine aerosol in the Bellingshausen Sea of the western Antarctic is coupled to the environment. Processes driving marine aerosol include wind speed, which produces sea spray aerosol (SSA), sea surface temperature (SST), which can enhance the production of SSA, and seasonal dynamics of sea ice melt and phytoplankton blooms, which can contribute to production of biogenic sources of marine aerosol. To study these drivers in closer detail, we used two specialized proxies of marine aerosol concentration: coarse‐mode Aerosol Optical Depth (AODC), a proxy for SSA, and Marine Aerosol Optical Depth (MAOD) a proxy for low‐altitude marine aerosol. We examined MAOD and AODCfrom 2007 to 2018 and found that wind speed was a driver of day‐to‐day fluxes in marine aerosol. In contrast to the tropical Pacific in which enhanced biological activity suppresses SSA particle production, we did not observe lessening of MAOD and AODCmagnitudes during the biologically productive austral summertime. In fact, summertime MAOD exhibited a weak significant correlation to daily wind speed in the coastal ocean despite a lack of significance in wintertime. This work enriches our knowledge of biotic and abiotic drivers of marine aerosol in high‐latitude environments. The open ocean and coastal Bellingshausen Sea show weak correlations of marine aerosol optical depth (MAOD) to daily windsAODCexhibits weak correlations to sea surface temperature (SST) in the open ocean and very weak correlations to daily wind speed across all regionsSeasonal increases in MAOD dependence on daily wind speed is likely associated with higher biological activity in summer The open ocean and coastal Bellingshausen Sea show weak correlations of marine aerosol optical depth (MAOD) to daily winds AODCexhibits weak correlations to sea surface temperature (SST) in the open ocean and very weak correlations to daily wind speed across all regions Seasonal increases in MAOD dependence on daily wind speed is likely associated with higher biological activity in summer

This study presents seasonal trends in marine tropospheric aerosol arising from the interplay between physical and biological processes in the Western Antarctic Peninsula (WAP). Remote sensing‐based studies focused on aerosol distribution and links to chlorophyll‐aconcentration and sea ice predominantly use passive sensor retrievals of aerosol optical properties. However, these data are subject to cloud presence, signal uncertainties, and lack of retrievals in high latitude wintertime. To address these concerns, we have developed a method of quantifying tropospheric marine aerosol with the NASA Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), which we term marine aerosol optical depth (MAOD). MAOD may be retrieved in nighttime conditions of high‐latitude winter and is devoid of cloud contamination, thereby advancing upon prior aerosol optical depth (AOD) measurements linked with biogenic aerosol. To examine trends in tropospheric marine aerosol, we undertook a multi‐year remote sensing analysis in the Bellingshausen Sea from 2006 to 2018. A seasonal increase in MAOD was observed alongside a seasonal increase in chl‐aand sea ice melt, suggesting a biogenic component to aerosol presence. To the best of our knowledge, this study is also the first to further distinguish a late winter to early spring temporal MAOD signal, likely tied to an aerosol source from either venting of biogenic aerosol from breaks in sea ice or to sea spray/salt aerosol resulting from pulses in wind speed. Our work extends upon previous findings of AOD in polar environments and now more fully characterizes interactions during polar winter. Tropospheric marine aerosol presence in the western Antarctic is coupled to physical and biological processes. These aerosols may be biogenic, formed from the activity of primary producers, and can be associated with seasonal dynamics of sea ice melt and phytoplankton blooms. These aerosols may also influence local environments of polar regions by absorbing and scattering solar radiation and by initiating cloud formation. To study tropospheric marine aerosol in the remote marine Bellingshausen Sea environment, we used a specialized instrument onboard the NASA Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) capable of detecting the presence of aerosols at altitudes close to the sea surface. We termed this measurement marine aerosol optical depth (MAOD) and examined MAOD from 2006 to 2018. We found that the presence of aerosol increases alongside blooms of phytoplankton and sea ice melt, as predicted from prior studies, suggesting a biological source. We also find an increase in aerosol that may be linked to degassing of biogenic aerosol or seasonal increases in wind speed, which may indicate the presence of sea spray or sea salt. This work enriches our knowledge of the interwoven relationship between the surface ocean and the overlying atmosphere in this region of our planet. Marine aerosol optical depth (MAOD) retrieved by CALIPSO is used to quantify trends in marine tropospheric aerosol over Western AntarcticaIncreases in MAOD are tied to the seasonal melt of sea ice and the biomass of primary producers, suggesting a biogenic aerosol sourceMAOD is examined in high latitude winter, thereby advancing on optical depth observations from prior passive remote sensing measurements Marine aerosol optical depth (MAOD) retrieved by CALIPSO is used to quantify trends in marine tropospheric aerosol over Western Antarctica Increases in MAOD are tied to the seasonal melt of sea ice and the biomass of primary producers, suggesting a biogenic aerosol source MAOD is examined in high latitude winter, thereby advancing on optical depth observations from prior passive remote sensing measurements

The cyclic hydroxamate, 2,4‐dihydroxy.7‐methoxy‐l,4‐benzoxazin‐ 3‐one (DIMBOA), has been implicated in the resistance of corn (Zea maysL.) to fungi and insects. In our study, bioassay and field experiments tested the relationship between hydroxamate concentration and resistance to corn leaf aphid (Rhopalosiphum maidis(Fitch)). In the bioassay, various concentrattons of DIMBOA were added to an artificial diet fed to corn leaf aphids. DIMBOA concentrations of 0.1, 0.25, and 0.5 mg/g diet caused 5.1, 12.8, and 20.8% mortality, respectively. In field trials, 12 inbred lines were evaluated for corn leaf aphid resistance under natural infestation. Aphid infestation was evaluated at mid‐silking stage with a visual rating scale and index system. Cyclic hydroxamate concentration in a separate set of the same lines was estimated by a rapid procedure based upon the colorimetric reaction of hydroxamates with ferric chloride. Aphid infestation values ranged from 119 to 366. Hydroxamate concentration ranged from 0.08 to 1.48 mg/g fresh weight. A highly significant correlation (r = 0.72) was obtained between aphid infestation and hydroxamate concentration. Eighteen hybrids derived from crosses among 12 inbred lines were also evaluated for corn leaf aphid resistance in the field. Aphid infestation values from high ✕ high, intermediate ✕ intermediate, and low ✕ low DIMBOA lines were generally low, intermediate, and high, respectively. Hybrids derived from crossing high ✕ low, high ✕ intermediate, and intermediate ✕ low DIMBOA lines produced infestation values between the parental extremes.

Field experiments were conducted to determine the relationship between hydroxamic acid, total phenol, and orthodihydroxyphenol concentrations in corn (Zea maysL.) tassels and resistance to the corn leaf aphid [Rhopalosiphum maidis(Fitch)]. Eleven corn inbreds were evaluated for aphid resistance soon after tassel emergence using a visual rating scale and index system. The corn tassels were harvested and analyzed for hydroxamic acid, total phenol, and orthodihydroxyphenol content. A highly significant negative correlation (r = −0.63) was obtained between aphid infestation and hydroxamic acid concentration. Poor correlations were found between aphid infestation and both the total phenol and orthodihydroxyphenol concentrations. Seven corn inbred lines were further evaluated for corn leaf aphid resistance by artificial infestation in the greenhouse. A highly significant correlation (r = 0.90) was found between the greenhouse and field results.

The oxidative and hydrolytic metabolism of Thimet by plants, insects and mammals were further studied with chromatographic and radiotracer techniques. Bean plants, southern army worms (Prodenia eridania (Cram.)), albino rats, and a cow were utilized. The proportions of Thimet, oxidized derivatives, and hydrolysis products were determined with bean plants which had absorbed Thimet through their roots, with armyworms which had fed on these plants, and with the feces of the armyworms. Armyworms were more efficient than bean plants in vivo in oxidation of the phosphorothioate group of Thimet and in hydrolysis of the oxidation products. With the mammals, the excretory products and tissue residues were investigated. Extreme difficulty was encountered in extraction of the radioactivity from the tissues of the treated rats and cow. The relative insect and mammalian toxicity and stability to hydrolysis by alkali are reported for Thimet and its oxidation products.

From preliminary screening of 14 systemic compounds with cacao seedlings in Costa Rica, Thimet, Chipman R-6200 (0,0-diethyl S-(2-diethylamino)ethyl phosphorothiolate), demeton, Isolan and dimefox were selected for further study. These five systemics were compared on the basis of their translocation and persistence in the foliar parts of mature cacao trees after trunk implantation, their effect on the flavor of chocolate produced from beans from the treated trees, and the level and nature of residues in the beans using radiotracer and anticholinesterase methods of analysis. Thimet and Chipman R-6200 were readily translocated into the foliar portions of cacao trees and persisted for as long as 20 months after a single implantation treatment. Little or no residues were found in the cacao beans at any time after treatment regardless of the pod position on the trees in relation to the site of implantation. Studies with radioactive R-6200 demonstrated a high concentration of phosphorus-containing residues in the cotyledons of the cacao beans but these materials did not partition into chloroform and did not inhibit cholinesterase and therefore cannot be considered as hazardous residues. No off flavors were detected in chocolate from beans harvested from any of the systemic treatments but definite off-flavors were obtained when BHC was used as a foliar spray. The insecticidal efficiency of the systemics was not studied because the insect populations in the treated areas were not adequate for this purpose.