Melanie Gault-Ringold | University of Otago (original) (raw)

Uploads

Papers by Melanie Gault-Ringold

Research paper thumbnail of Anomalous isotopic shifts associated with organic resin residues during cadmium isotopic analysis by double spike MC-ICPMS

J. Anal. At. Spectrom., Jan 1, 2012

Previous studies have reported that matrix effects during analysis by multiple collector inductiv... more Previous studies have reported that matrix effects during analysis by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS), leading to highly anomalous isotopic results, can be derived from ion exchange separation procedures, as resin-...

Research paper thumbnail of A Common Reference Material for Cadmium Isotope Studies–NIST SRM 3108

Geostandards and …, Jan 1, 2012

Research paper thumbnail of Anomalous biogeochemical behavior of cadmium in subantarctic surface waters: Mechanistic constraints from cadmium isotopes

Earth and Planetary …, Jan 1, 2012

The user has requested enhancement of the downloaded file. All in-text references underlined in b... more The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately.

Research paper thumbnail of The Marine Biogeochemisty of Cadmium: Studies of Cadmium Isotopic Variations in the Southern Ocean

Cadmium (Cd) in the oceans closely mimics the behavior of the macronutrient phosphate ) and can b... more Cadmium (Cd) in the oceans closely mimics the behavior of the macronutrient phosphate ) and can be used in the enzyme carbonic anhydrase (CA), suggesting a biological uptake of Cd. This relationship between Cd and PO 4 3has been used extensively as a paleoproxy for historic nutrient cycling. However, the validity of this proxy is questionable due to the complexity of the Cd /PO 4 3relationship. To this end, Cd isotopic studies can provide critical insight into the mechanism controlling Cd uptake and may, in itself, be a First I would like to thank my supervisors, Claudine Stirling, Russell Frew, and Keith Hunter. Thank you all for the many intense hours of thesis reading over the last weeks. This would not have been possible without your comments, advice, and support. Thank you Claudine for being our FILTER boss, all of your advice both in the lab and in life over the past four years was invaluable. Thank you for being enthusiastic throughout the entire process, without you, I may have given up long ago. Thank you Russell for the many impromptu discussions and brainstorming about the oceans, and I always appreciate our talks about farming and lambs. Thank you Keith for building such an amazing research group and accepting me to be a part of it. Waterworld"s knowledge of the oceans is incredible and has provided such a unique environment for the studies of marine biogeochemistry. Thank you for your enthusiasm about science and the numerous hours that you made available for me. Thank you to the three examiners, Michael Ellwood, Ken Bruland and Sylvia Sander for the time and energy spent reading this thesis and making corrections. All of your comments are discussion are very much appreciated. Thank you to Frank Wombacher, Joel Baker, and Mark Rehkamper for providing cadmium standards and double spike advice, aiding in the positive outcomes of this research. I would like to thank all of my past and present colleagues from Waterworld and the chemistry department for all of their help, brainstorming, motivation and enthusiasm for the work we are doing, including: Especially to Malcolm Reid for all of your help on the mass spec and all aspects of the lab and science. As our FILTER solution, you were always there to help me solve my problems. To Evelyn Armstrong, Eike Breitbarth and Linn Hoffmann for all of your help with my phytoplankton culturing when my lack of a green thumb shone through. And to Robert Strzepek for all of the help and advice and for making this culture work possible. Thank you to Kim Curry for organizing every sampling trip and helping through the hours of seasickness and frustrations of compressors, pumps, and tubing that seemed to be inevitable no matter how organized we were. And especially to Bill Dixon and Phil Heseltine, the captain and crewman of the R/V Polaris II, for being patient, and more than helpful in every aspect of the sampling process. Thank you to Hugh Doyle for being seasick with/for me, more than anyone else. Thank you to Katherine Baer and Sylvia Sander for their friendship and helping keep me healthy, or at least trying to, on all of our lunchtime runs. Thank you especially to my FILTER girls, Martine Poffet, Mihoko Numata, and Angela Kaltenbach. I could not have asked for better friends to share a lab with. The hours of lunches, coffee breaks, weekends, bbq"s, and camping trips will never be forgotten. To my parents, Carol Gault and Gordon Ringold and the rest of my family, thank you for supporting me throughout my life and helping me get to this point. I could not have done this without your love and encouragement. To my friends from all over the world, thank you for not giving up on me, despite my thesis brain and my lack of communication over the last year.

Research paper thumbnail of Cadmium Isotopic Compositions and Nutrient Cycling in the Southern Ocean

… et Cosmochimica Acta …, Jan 1, 2009

Cadmium (Cd) in conjunction with phosphate (PO4) has been used as a paleoproxy for understanding ... more Cadmium (Cd) in conjunction with phosphate (PO4) has been used as a paleoproxy for understanding nutrient cycling in historic oceans. However, our limited knowledge of Cd biogeochemical cycling in the oceans has led to many assumptions being used in the application of the Cd/PO4 ...

Research paper thumbnail of Mercury speciation in Pacific coastal rainwater, Monterey Bay, California

Atmospheric …, Jan 1, 2010

We measured mercury speciation in coastal rainwater samples from Monterey Bay, California in 2007... more We measured mercury speciation in coastal rainwater samples from Monterey Bay, California in 2007e2008 to investigate the source of monomethylmercury (MMHg) in rainwater and determine the relative importance of wet atmospheric deposition of MMHg to coastal waters compared to other sources on the central Pacific coast. Total mercury (HgT) ranged from 10 to 88 pM, with a sample mean AE standard deviation of 33 AE 22 pM (volume-weighted average 29 pM). MMHg concentrations ranged from 0.12 to 2.3 pM with a sample mean of 0.7 AE 0.5 pM (volume-weighted average 0.68 pM). Reactive mercury (HgR) concentrations ranged from 0.87 to 47 pM, sample mean 7.8 AE 8.3 pM (volume-weighted average 6.1 pM). Acetate concentration in rainwater, measured in a subset of samples, ranged from 0.34 to 3.1 mM, and averaged 1.6 AE 0.9 mM (volume-weighted average 1.3 mM). Dimethylmercury (DMHg) concentrations were below the limit of detection in air (<0.01 ng m À3 ) and rainwater (<0.05 pM). Despite previous suggestions that DMHg in upwelled ocean waters is a potential source of MMHg in coastal rainwater, MMHg in rain was not related to coastal upwelling seasons or surface water DMHg concentrations. Instead, a multiple linear regression analysis demonstrated that MMHg concentrations were positively and significantly correlated (p ¼ 0.002, adjusted R 2 ¼ 0.88) with those of acetate and HgR. These data appear to support previous suggestions that the aqueous phase methylation of Hg(II) by acetate may be the source of MMHg in rainwater, but imply that acetate concentrations in rainwater play a more important role relative to HgR than previously hypothesized. However, the calculated chemical speciation of Hg(II) in rainwater and the minimal predicted complexation of Hg(II) by acetate suggest that the aqueous phase methylation of Hg(II) by acetate is unlikely to account for the MMHg found in precipitation, or that the mechanism of this reaction in the atmosphere differs from that previously reported .

Research paper thumbnail of Dimethylmercury in Coastal Upwelling Waters, Monterey Bay, California

Environmental …, Jan 1, 2009

Depth profiles of dimethylmercury (DMHg) concentration were determined at nearshore to offshore s... more Depth profiles of dimethylmercury (DMHg) concentration were determined at nearshore to offshore sites in Monterey Bay, California. The onset of spring upwelling in the bay was accompanied by increases in DMHg concentrations. Profiles show DMHg increasing gradually with depth in fall and winter from &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.03 pM at the surface to 0.5 pM at 200 m. During the spring, DMHg concentrations increased between 30 and 100 m, first within Monterey Bay, then offshore. This change was accompanied by an increase in DMHg concentrations in the surface water DMHg between fall/winter (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.03 pM) and spring (0.06-0.29 pM). Microbial activity associated with the remineralization of sinking organic matter produced by the high primary production in the bay may result in the relatively high DMHg in subsurface water in the bay, which when upwelled may facilitate the incorporation of organomercury into biota. As a result, productive coastal upwelling areas may represent an important source of methylated mercury to surface waters, and thus be an important source of mercury to marine ecosystems.

Research paper thumbnail of Anomalous isotopic shifts associated with organic resin residues during cadmium isotopic analysis by double spike MC-ICPMS

J. Anal. At. Spectrom., Jan 1, 2012

Previous studies have reported that matrix effects during analysis by multiple collector inductiv... more Previous studies have reported that matrix effects during analysis by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS), leading to highly anomalous isotopic results, can be derived from ion exchange separation procedures, as resin-...

Research paper thumbnail of A Common Reference Material for Cadmium Isotope Studies–NIST SRM 3108

Geostandards and …, Jan 1, 2012

Research paper thumbnail of Anomalous biogeochemical behavior of cadmium in subantarctic surface waters: Mechanistic constraints from cadmium isotopes

Earth and Planetary …, Jan 1, 2012

The user has requested enhancement of the downloaded file. All in-text references underlined in b... more The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately.

Research paper thumbnail of The Marine Biogeochemisty of Cadmium: Studies of Cadmium Isotopic Variations in the Southern Ocean

Cadmium (Cd) in the oceans closely mimics the behavior of the macronutrient phosphate ) and can b... more Cadmium (Cd) in the oceans closely mimics the behavior of the macronutrient phosphate ) and can be used in the enzyme carbonic anhydrase (CA), suggesting a biological uptake of Cd. This relationship between Cd and PO 4 3has been used extensively as a paleoproxy for historic nutrient cycling. However, the validity of this proxy is questionable due to the complexity of the Cd /PO 4 3relationship. To this end, Cd isotopic studies can provide critical insight into the mechanism controlling Cd uptake and may, in itself, be a First I would like to thank my supervisors, Claudine Stirling, Russell Frew, and Keith Hunter. Thank you all for the many intense hours of thesis reading over the last weeks. This would not have been possible without your comments, advice, and support. Thank you Claudine for being our FILTER boss, all of your advice both in the lab and in life over the past four years was invaluable. Thank you for being enthusiastic throughout the entire process, without you, I may have given up long ago. Thank you Russell for the many impromptu discussions and brainstorming about the oceans, and I always appreciate our talks about farming and lambs. Thank you Keith for building such an amazing research group and accepting me to be a part of it. Waterworld"s knowledge of the oceans is incredible and has provided such a unique environment for the studies of marine biogeochemistry. Thank you for your enthusiasm about science and the numerous hours that you made available for me. Thank you to the three examiners, Michael Ellwood, Ken Bruland and Sylvia Sander for the time and energy spent reading this thesis and making corrections. All of your comments are discussion are very much appreciated. Thank you to Frank Wombacher, Joel Baker, and Mark Rehkamper for providing cadmium standards and double spike advice, aiding in the positive outcomes of this research. I would like to thank all of my past and present colleagues from Waterworld and the chemistry department for all of their help, brainstorming, motivation and enthusiasm for the work we are doing, including: Especially to Malcolm Reid for all of your help on the mass spec and all aspects of the lab and science. As our FILTER solution, you were always there to help me solve my problems. To Evelyn Armstrong, Eike Breitbarth and Linn Hoffmann for all of your help with my phytoplankton culturing when my lack of a green thumb shone through. And to Robert Strzepek for all of the help and advice and for making this culture work possible. Thank you to Kim Curry for organizing every sampling trip and helping through the hours of seasickness and frustrations of compressors, pumps, and tubing that seemed to be inevitable no matter how organized we were. And especially to Bill Dixon and Phil Heseltine, the captain and crewman of the R/V Polaris II, for being patient, and more than helpful in every aspect of the sampling process. Thank you to Hugh Doyle for being seasick with/for me, more than anyone else. Thank you to Katherine Baer and Sylvia Sander for their friendship and helping keep me healthy, or at least trying to, on all of our lunchtime runs. Thank you especially to my FILTER girls, Martine Poffet, Mihoko Numata, and Angela Kaltenbach. I could not have asked for better friends to share a lab with. The hours of lunches, coffee breaks, weekends, bbq"s, and camping trips will never be forgotten. To my parents, Carol Gault and Gordon Ringold and the rest of my family, thank you for supporting me throughout my life and helping me get to this point. I could not have done this without your love and encouragement. To my friends from all over the world, thank you for not giving up on me, despite my thesis brain and my lack of communication over the last year.

Research paper thumbnail of Cadmium Isotopic Compositions and Nutrient Cycling in the Southern Ocean

… et Cosmochimica Acta …, Jan 1, 2009

Cadmium (Cd) in conjunction with phosphate (PO4) has been used as a paleoproxy for understanding ... more Cadmium (Cd) in conjunction with phosphate (PO4) has been used as a paleoproxy for understanding nutrient cycling in historic oceans. However, our limited knowledge of Cd biogeochemical cycling in the oceans has led to many assumptions being used in the application of the Cd/PO4 ...

Research paper thumbnail of Mercury speciation in Pacific coastal rainwater, Monterey Bay, California

Atmospheric …, Jan 1, 2010

We measured mercury speciation in coastal rainwater samples from Monterey Bay, California in 2007... more We measured mercury speciation in coastal rainwater samples from Monterey Bay, California in 2007e2008 to investigate the source of monomethylmercury (MMHg) in rainwater and determine the relative importance of wet atmospheric deposition of MMHg to coastal waters compared to other sources on the central Pacific coast. Total mercury (HgT) ranged from 10 to 88 pM, with a sample mean AE standard deviation of 33 AE 22 pM (volume-weighted average 29 pM). MMHg concentrations ranged from 0.12 to 2.3 pM with a sample mean of 0.7 AE 0.5 pM (volume-weighted average 0.68 pM). Reactive mercury (HgR) concentrations ranged from 0.87 to 47 pM, sample mean 7.8 AE 8.3 pM (volume-weighted average 6.1 pM). Acetate concentration in rainwater, measured in a subset of samples, ranged from 0.34 to 3.1 mM, and averaged 1.6 AE 0.9 mM (volume-weighted average 1.3 mM). Dimethylmercury (DMHg) concentrations were below the limit of detection in air (<0.01 ng m À3 ) and rainwater (<0.05 pM). Despite previous suggestions that DMHg in upwelled ocean waters is a potential source of MMHg in coastal rainwater, MMHg in rain was not related to coastal upwelling seasons or surface water DMHg concentrations. Instead, a multiple linear regression analysis demonstrated that MMHg concentrations were positively and significantly correlated (p ¼ 0.002, adjusted R 2 ¼ 0.88) with those of acetate and HgR. These data appear to support previous suggestions that the aqueous phase methylation of Hg(II) by acetate may be the source of MMHg in rainwater, but imply that acetate concentrations in rainwater play a more important role relative to HgR than previously hypothesized. However, the calculated chemical speciation of Hg(II) in rainwater and the minimal predicted complexation of Hg(II) by acetate suggest that the aqueous phase methylation of Hg(II) by acetate is unlikely to account for the MMHg found in precipitation, or that the mechanism of this reaction in the atmosphere differs from that previously reported .

Research paper thumbnail of Dimethylmercury in Coastal Upwelling Waters, Monterey Bay, California

Environmental …, Jan 1, 2009

Depth profiles of dimethylmercury (DMHg) concentration were determined at nearshore to offshore s... more Depth profiles of dimethylmercury (DMHg) concentration were determined at nearshore to offshore sites in Monterey Bay, California. The onset of spring upwelling in the bay was accompanied by increases in DMHg concentrations. Profiles show DMHg increasing gradually with depth in fall and winter from &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.03 pM at the surface to 0.5 pM at 200 m. During the spring, DMHg concentrations increased between 30 and 100 m, first within Monterey Bay, then offshore. This change was accompanied by an increase in DMHg concentrations in the surface water DMHg between fall/winter (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.03 pM) and spring (0.06-0.29 pM). Microbial activity associated with the remineralization of sinking organic matter produced by the high primary production in the bay may result in the relatively high DMHg in subsurface water in the bay, which when upwelled may facilitate the incorporation of organomercury into biota. As a result, productive coastal upwelling areas may represent an important source of methylated mercury to surface waters, and thus be an important source of mercury to marine ecosystems.