Pamela Barrett - Academia.edu (original) (raw)

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Sujit Sen

National Institute of Technology Rourkela

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Papers by Pamela Barrett

Marine Chemistry, 2015

ABSTRACT Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples ... more ABSTRACT Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples from the upper 1000 m of the eastern North Atlantic Ocean along the CLIVAR/CO2 Repeat Hydrography program section A16N in summer 2013, repeating trace metal observations made along the A16N transect a decade earlier. Upper-ocean trace metal distributions in the equatorial and subtropical regions of the North Atlantic are heavily influenced by atmospheric aerosol sources. Using changes in the concentrations of subsurface particulate Al and Fe and mixed-layer dissolved Al in the equatorial North Atlantic, we estimate dust deposition to surface waters in the eastern North Atlantic increased by approximately 15% between 2003 and 2013. Increased concentrations of dissolved Al in subtropical mode waters suggest that dust deposition may have also increased in the western basin. Our observations are consistent with recent reports linking increasing sea surface temperatures in the tropical North Atlantic to increased removal of atmospheric dust via precipitation over the past several decades and highlight the importance of accurate representation of dust deposition processes for modelling Fe biogeochemistry.

Global Biogeochemical Cycles, 2015

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along~95°E

Global Biogeochemical Cycles, 2014

ABSTRACT Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water... more ABSTRACT Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water column of the ocean (< 1500 m). This study uses the distribution of particulate calcium from high-resolution suspended matter sampling along the CLIVAR/CO2 Repeat Hydrography A16N transect in 2003 to estimate CaCO3 dissolution in the top 1000 m of the North Atlantic. Dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces. Water masses were found to be undersaturated with respect to aragonite at intermediate depths (400–1000 m) in the eastern tropical North Atlantic. The CaCO3 dissolution rate in this region is estimated to be 0.9 mmol CaCO3 m-2 d-1, indicating this region is a hotspot for upper water column CaCO3 dissolution compared to the Atlantic basin as a whole. Dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower (0.2 mmol CaCO3 m-2 d-1) and are comparable to previous estimates of CaCO3 dissolution flux for the Atlantic Ocean. The magnitude of upper water column dissolution rates compared to measured surface-ocean CaCO3 standing stocks suggests that biologically-mediated CaCO3 dissolution may be occurring in the top 1000 m of the Atlantic.

Inorganic Chemistry, 2009

A series of three-and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sul... more A series of three-and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant of the neutral ligands, and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in K eq , which decrease in the order CN t Bu > pyridine > 2-picoline > DMF > MeCN > THF > PPh 3 . These differences can be attributed to a mixture of steric effects and electronic effects (both σ and π). The binding constants and the reduction potentials are surprisingly insensitive to changes in an anionic spectator ligand. This suggests that three-coordinate iron(II) complexes may have similar binding trends as proposed three-coordinate iron(II) intermediates in the FeMoco of nitrogenase, even though the anionic spectator ligands in the synthetic complexes differ from the sulfides in the FeMoco. *holland@chem.rochester.edu. Supporting Information available: Details of NMR spectra, equilibrium measurements, cyclic voltammetry, and solid angle calculation (PDF) and crystallography (CIF). This material is available free of charge via the Internet at

Marine Chemistry, 2015

ABSTRACT Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples ... more ABSTRACT Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples from the upper 1000 m of the eastern North Atlantic Ocean along the CLIVAR/CO2 Repeat Hydrography program section A16N in summer 2013, repeating trace metal observations made along the A16N transect a decade earlier. Upper-ocean trace metal distributions in the equatorial and subtropical regions of the North Atlantic are heavily influenced by atmospheric aerosol sources. Using changes in the concentrations of subsurface particulate Al and Fe and mixed-layer dissolved Al in the equatorial North Atlantic, we estimate dust deposition to surface waters in the eastern North Atlantic increased by approximately 15% between 2003 and 2013. Increased concentrations of dissolved Al in subtropical mode waters suggest that dust deposition may have also increased in the western basin. Our observations are consistent with recent reports linking increasing sea surface temperatures in the tropical North Atlantic to increased removal of atmospheric dust via precipitation over the past several decades and highlight the importance of accurate representation of dust deposition processes for modelling Fe biogeochemistry.

Global Biogeochemical Cycles, 2015

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along~95°E

Global Biogeochemical Cycles, 2014

ABSTRACT Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water... more ABSTRACT Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water column of the ocean (< 1500 m). This study uses the distribution of particulate calcium from high-resolution suspended matter sampling along the CLIVAR/CO2 Repeat Hydrography A16N transect in 2003 to estimate CaCO3 dissolution in the top 1000 m of the North Atlantic. Dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces. Water masses were found to be undersaturated with respect to aragonite at intermediate depths (400–1000 m) in the eastern tropical North Atlantic. The CaCO3 dissolution rate in this region is estimated to be 0.9 mmol CaCO3 m-2 d-1, indicating this region is a hotspot for upper water column CaCO3 dissolution compared to the Atlantic basin as a whole. Dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower (0.2 mmol CaCO3 m-2 d-1) and are comparable to previous estimates of CaCO3 dissolution flux for the Atlantic Ocean. The magnitude of upper water column dissolution rates compared to measured surface-ocean CaCO3 standing stocks suggests that biologically-mediated CaCO3 dissolution may be occurring in the top 1000 m of the Atlantic.

Inorganic Chemistry, 2009

A series of three-and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sul... more A series of three-and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant of the neutral ligands, and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in K eq , which decrease in the order CN t Bu > pyridine > 2-picoline > DMF > MeCN > THF > PPh 3 . These differences can be attributed to a mixture of steric effects and electronic effects (both σ and π). The binding constants and the reduction potentials are surprisingly insensitive to changes in an anionic spectator ligand. This suggests that three-coordinate iron(II) complexes may have similar binding trends as proposed three-coordinate iron(II) intermediates in the FeMoco of nitrogenase, even though the anionic spectator ligands in the synthetic complexes differ from the sulfides in the FeMoco. *holland@chem.rochester.edu. Supporting Information available: Details of NMR spectra, equilibrium measurements, cyclic voltammetry, and solid angle calculation (PDF) and crystallography (CIF). This material is available free of charge via the Internet at

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