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Karen Casciotti

Publications and source records attributed to Karen Casciotti.

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Perspectives on chemical oceanography in the 21st century: Participants of the COME ABOARD Meeting examine aspects of the field in the context of 40 years of DISCO

The questions that chemical oceanographers prioritize over the coming decades, and the methods we use to address these questions, will define our field's contribution to 21st century science. In recognition of this, the U.S. National Science Foundation and National Oceanic and Atmospheric Administration galvanized a community effort (the Chemical Oceanography MEeting: A BOttom-up Approach to Research Directions, or COME ABOARD) to synthesize bottom-up perspectives on selected areas of research in Chemical Oceanography. Representing only a small subset of the community, COME ABOARD participants did not attempt to identify targeted research directions for the field. Instead, we focused on how best to foster diverse research in Chemical Oceanography, placing emphasis on the following themes: strengthening our core chemical skillset; expanding our tools through collaboration with chemists, engineers, and computer scientists; considering new roles for large programs; enhancing interface research through interdisciplinary collaboration; and expanding ocean literacy by engaging with the public. For each theme, COME ABOARD participants reflected on the present state of Chemical Oceanography, where the community hopes to go and why, and actionable pathways to get there. A unifying concept among the discussions was that dissimilar funding structures and metrics of success may be required to accommodate the various levels of readiness and stages of knowledge development found throughout our community. In addition to the science, participants of the concurrent Dissertations Symposium in Chemical Oceanography (DISCO) XXV, a meeting of recent and forthcoming Ph.D. graduates in Chemical Oceanography, provided perspectives on how our field could show leadership in addressing long-standing diversity and early-career challenges that are pervasive throughout science. Here we summarize the COME ABOARD Meeting discussions, providing a synthesis of reflections and perspectives on the field.

Marine Chemistry

Determination of the δ 15 N of nitrate in solids; RSIL lab code 2894

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2894 is to determine the δ 15 N of nitrate (NO 3 - ) in solids. The nitrate fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2899. After leaching, the δ 15 N of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods

Determination of the δ 15 N and δ 18 O of nitrate in solids; RSIL lab code 2897

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2897 is to determine the δ 15 N and δ 18 O of nitrate (NO 3 - ) in solids. The NO 3 - fraction of the nitrogen species is dissolved by water (called leaching) and can be analyzed by the bacterial method covered in RSIL lab code 2900. After leaching, the δ 15 N and δ 18 O of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods

Determination of the δ 15 N of nitrate in water; RSIL lab code 2899

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2899 is to determine the δ 15 N of nitrate (NO 3 - ) in water. The δ 15 N of the dissolved NO 3 - is analyzed by conversion of the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods

Determination of the δ 15 N and δ 18 O of nitrate in water; RSIL lab code 2900

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2900 is to determine the δ 15 N and δ 18 O of nitrate (NO 3 - ) in water. The δ 15 N and δ 18 O of the dissolved NO 3 - are analyzed by converting the NO 3 - to nitrous oxide (N 2 O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of the NO 3 - to N 2 O, which follows the pathway shown in equation 1: NO 3 - → NO 2 - → NO → 1/2 N 2 O (1) Because the bacteria Pseudomonas aureofaciens lack N 2 O reductive activity, the reaction stops at N 2 O, unlike the typical denitrification reaction that goes to N 2 . After several hours, the conversion is complete, and the N 2 O is extracted from the vial, separated from volatile organic vapor and water vapor by an automated -65 °C isopropanol-slush trap, a Nafion drier, a CO 2 and water removal unit (Costech #021020 carbon dioxide absorbent with Mg(ClO 4 ) 2 ), and trapped in a small-volume trap immersed in liquid nitrogen with a modified Finnigan MAT (now Thermo Scientific) GasBench 2 introduction system. After the N 2 O is released, it is further purified by gas chromatography before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Thermo Scientific Delta V Plus continuous flow IRMS (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge ( m/z ) of the N 2 O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N 2 O = 14 N 14 N 16 O; m/z = 45 = N 2 O = 14 N 15 N 16 O or 14 N 14 N 17 O; m/z = 46 = N 2 O = 14 N 14 N 18 O. The 17 O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ 15 N values are reported.

Techniques and Methods