What can paired measurements of Th isotope activity and particle concentration tell us about particle cycling in the ocean?

Marchal, Olivier; Lam, Phoebe J.

doi:10.1016/j.gca.2012.05.009

Cited by 28 publications

(33 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Alternatively, 230 Th concentration anomalies in profile may be smoothed by vertical mixing, as 230 Th displays larger depth gradients in concentration than the other Th isotopes. Future size-fractionated Th isotope studies in seawater will inform us about differing removal rates among the thorium isotopes (Marchal and Lam, 2012). For instance, the high depth-resolution 234 Th-232 Th-230 Th-228 Th data being collected by the GEOTRACES program will help test the hypothesis that each dissolved Th isotope is subject to similar removal rates.…”

Section: Thorium Cyclingmentioning

confidence: 99%

Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes

Hayes

Anderson

Fleisher

et al. 2013

Earth and Planetary Science Letters

View full text Add to dashboard Cite

Dissolved 232 Th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as Fe. Oceanic 230 Th, on the other hand, is sourced primarily from the highly predictable decay of dissolved 234 U. The rate at which dissolved 232 Th is released by mineral dissolution can be constrained by a Th removal rate derived from 230 Th: 234 U disequilibria, assuming steady-state. Calculated fluxes of dissolved 232 Th can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies, such as aerosol dust deposition, given the concentration and fractional solubility of Th (or other metals) in the lithogenic material. This method is applied to 7 water column profiles from the Innovative North Pacific Experiment (INOPEX) cruise of 2009 and 2 sites from the subtropical North Pacific. The structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved 232 Th at 100-200 m depth. This rapid cycling could involve colloidal Th generated during mineral dissolution, which may not be subject to the same removal rates as the more truly dissolved 230 Th. An additional deep source of 232 Th was revealed in deep waters, most likely dissolution of seafloor sediments, and offers a constraint on dissolved trace element supply due to boundary exchange.

show abstract

Section: Thorium Cyclingmentioning

confidence: 99%

Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes

Hayes

Anderson

Fleisher

et al. 2013

Earth and Planetary Science Letters

View full text Add to dashboard Cite

show abstract

“…Marchal and Lam (2012) demonstrated that the GEOTRACES programs are well poised to improve estimates of rates of adsorption, desorption, remineralization and aggregation of small particles, and disaggregation and sinking of larger particles in the ocean. The US GEOTRACES program can provide data of 234 Th,228 Th, and 230 Th with good depth resolution and in the dissolved phase and two particulate size classes.…”

Section: Th From Geotraces Transects Of the Atlantic Oceanmentioning

confidence: 99%

Advances in measurements of particle cycling and fluxes in the ocean

Owens¹

2013

View full text Add to dashboard Cite

The sinking flux of particles is an important removal mechanism of carbon from the surface ocean as part of the biological pump and can play a role in cycling of other chemical species. This work dealt with improving methods of measuring particle export and measuring export on different scales to assess its spatial variability. First, the assumption of 238 U linearity with salinity, used in the 238 U-234 Th method, was reevaluated using a large sample set over a wide salinity range. Next, neutrally buoyant and surfacetethered sediment traps were compared during a three-year time series in the subtropical Atlantic. This study suggested that previously observed imbalances between carbon stocks and fluxes in this region are not due to undersampling by traps. To assess regional variability of particle export, surface and water-column measurements of 234 Th were combined for the first time to measure fluxes on ~20 km scales. Attempts to relate surface properties to particle export were complicated by the temporal decoupling of production and export. Finally, particle export from 234 Th was measured on transects of the Atlantic Ocean to evaluate basin-scale export variability. High-resolution sampling through the water-column allowed for the identification of unique 234 AcknowledgementsI feel so very lucky to have had the opportunity to work with my advisor, Ken Buesseler. Most graduate students are not required to travel extensively and spend weeks at sea with their advisors, but as an oceanography student, I was fortunate to have Ken as both a mentor and a friend. In addition to the many things Ken has taught me about science, I hope he has also instilled in me his skills of diplomacy that I got to witness for five years as his student. I also blame Ken, but thank him, for developing my interest in politics, particularly as it relates to science. Without his encouragement and support, I might not have had the courage to apply for my Knauss Fellowship. Outside of the office, I have to thank both Ken and his wife, Wendi, for being such good friends to Paul and myself. It was so special to have you be such an integral part of our wedding and I look to you as role models for our relationship.My secondary support system was my thesis committee, made up of Phoebe Lam, Dave Glover, and Mick Follows. Your continued support, suggestions, and encouragement over the last three years have helped me get to this point. Thank you also, to the chair of my defense, Carl Lamborg, for his support over my time at WHOI. In addition to those mentioned above, through various projects, I have had the opportunity to work with a large group of scientists whose support and assistance I appreciate including Ken Sims, Matthew Charette, Bill Jenkins, Rachel Stanley, Jim Valdes, Rod Johnson, Mike Lomas, Dave Siegel, Debbie Steinberg, Hugh Ducklow, Hein de Baar, Micha Rijkenberg, and Pere Masque. Those who I may have omitted here have been acknowledged in the relevant thesis chapters.My time at WHOI would not have been the same without th...

show abstract

“…Ordinary differential equations were solved using a Runge-Kutte ODE45 parameterization in MATLAB (MathWorks, Natick MA). (Marchal and Lam, 2012). Nevertheless, disaggregation rates…”

Section: Lithogenic Particle Cycling 1-d Model: Resultsmentioning

confidence: 99%

“…This is a simplified version of the conceptual models used to model scavenging and removal by particles of thorium isotopes (Clegg and Whitfield, 1993;Clegg et al, 1991;Marchal and Lam, 2012) that retains the particle dynamics terms only. We postulate that since Ti is relatively inert, we can ignore the scavenging and remineralization terms that transfer material between dissolved and small size fractions for simulating the concentration profiles of SSF and LSF pTi.…”

Section: Lithogenic Particle Cycling 1-d Model: Descriptionmentioning

confidence: 99%

The biogeochemistry of marine particulate trace metals

Ohnemus¹

2014

View full text Add to dashboard Cite

Marine particles include all living and non-living solid components of seawater, representing an extremely dynamic and chemically diverse mixture of phases. The distributions of these phases are poorly constrained and undersampled in the oceans, despite interactions between living organisms and non-living minerals having central roles within many globally relevant biogeochemical processes. Through a combination of method development, basin-scale particulate collection and analyses, modeling, and field experiments, this thesis examines both the distributions of marine particulate trace metals and the underlying processesinputs, scavenging, vertical and horizontal transport, and biotic uptake-in which marine particles participate.I first present the results of an intercalibration exercise among several US laboratories that analyzed filtered particles on shared polyethersulfone filters. We use inter-lab and intra-lab total elemental recoveries of these particles to determine our state of our intercalibration (521% one-sigma inter-lab uncertainty for most elements; 9% intra-lab) and to identify means of future improvement. We also present a new chemical method for complete dissolution of polyethersulfone filters and compare it to other total particle digestion procedures. I then present the marine particulate distributions of the lithogenic elements Al, Fe, and Ti in the North Atlantic GEOTRACES section. Inputs of lithogenic particles from African dust sources, hydrothermal systems, benthic nepheloid layers and laterally-sourced margin influences are observed and discussed. Lithogenic particle residence times, size-fractionation patterns, Ti-mineral speciation, and relationships to biological aggregation processes are calculated and described. A one-dimensional, sizefractionated, multi-box model that describes lithogenic particle distributions is also proposed and its parameter sensitivities and potential implications are discussed.The thesis concludes with the presentation of results from a series of bottle incubations in naturally iron-limited waters using isotopically labeled Fe-minerals. We demonstrate both biotic and abiotic solubilization of the minerals ferrihydrite and fayalite via transfer of isotopic label into suspended particles. These results are the first of their kind to demonstrate that minerals can be a source of bioavailable iron to euphotic communities and that spatial and ecological variations in mineral Fe-bioavailability may exist.Thesis supervisor: Phoebe J. Lam Title: Associate Scientist AcknowledgementsAlthough this thesis has my name on it, every page bears the watermark of my brilliant and ever thoughtful advisor, Phoebe (J.) Lam. Thank you so much for providing me with exciting projects, invigorating afternoon data conversations, prompt and thoughtful written feedback, and what I'm sure was a lifetime's worth of patience over the years. Together we've travelled to the bottom of the world, sampled oceans, and spent nights by the hum of a synchrotron; it's hard to imagine doing rese...

show abstract

What can paired measurements of Th isotope activity and particle concentration tell us about particle cycling in the ocean?

Cited by 28 publications

References 55 publications

Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes

Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes

Advances in measurements of particle cycling and fluxes in the ocean

The biogeochemistry of marine particulate trace metals

Contact Info

Product

Resources

About