Research Topics

This NSF funded research is now in its 9^th year as an Ocean Acidification study and collaborative project with J. Adkins and his group (Caltech)—our objective is to use novel geochemical approaches and new devices to examine carbonate dissolution kinetics–in the lab, in the field and in silico. This is actually a well-studied topic, yet there is disagreement in the field regarding the formulation of the dissolution rate equation. One of the issues we have overcome is determining slow dissolution rates that occur near saturation. We have grown biogenic and abiogenic particles under heavy ¹³C conditions, and can use this mineral to detect very small dissolution rates in <3 days. We are able to control saturation state in sea water by changing TA, we are also able to conduct experiments at different pressures, thus control saturation state by modifying K_sp. We have built a novel Niskin incubator device and used it successfully on a research cruise in the North Pacific Ocean (See papers by Subhas, Dong, Naviaux and Adkins et al. 2021). We have also studied dissolution kinetics using atomic force microscopy (papers by Dong) and are developing methods to apply SIMS analyses of carbonate as a metric of dissolution mechanism and rate.

W. Berelson and many other colleagues at USC are involved in studies of Urban air, soil and water quality. Berelson has particularly focused on urban CO2 and methane sources and sinks and has a rooftop sampling protocol that can monitor Los Angeles air at a very high temporal resolution. We measure CO2 concentrations and its isotopic composition and can extract information about the relative importance of petroleum vs. natural gas burning as CO2 sources. We are expanding this project to include other air constituents (Pietro Vannucci and Thaomy Vo), developing a network of sensors called the Carbon Census (Nick Rollins and Devan Roper), and targeting specific urban landscapes (Wenye Wang) to understand more deeply the urban built environment and ecosystem in terms of air quality. Students encouraged with interest in this topic.

We are working to define how sea water that is pumped through carbonate-poor sands change with respect to carbonate chemistry. We find that as ocean water acidifies via CO2 addition to our atmosphere, the carbonate minerals in sands will neutralize that acid, although this occurs as a function of residence time of water within the sand column. This work has been extended onto the continental shelf off Huntington Beach using our in situ pore water sampler, allowing us to determine how sandy continental shelf sediments are affecting ocean geochemistry and carbon cycling.

The Eastern Tropical South Pacific includes a zone of strong coastal upwelling, an intense OMZ and portions of the oligotrophic S. Pacific gyre. A group of us (D. Capone, USC; A. Knapp, FSU; K. Casciotti, Stanford) set out to determine N cycling in these waters, to examine if N fixation were an important contributor to production and export in this region. My contribution included measurements of Radon in surface waters as a tracer for gas exchange, measurements of underway O₂/Ar, deployment and measurement of particle fluxes to floating sediment traps, deployment and recovery of two deep sea sediment traps, and the determination and modeling of pore water nitrate and Si(OH)₄ profiles.

Papers/Manuscripts related to ETSP work:

Berelson et al. 2014; Haskell et al. 2013, 2014; Prokopenko et al. 2014; Knapp et al. 2014; Yeung et al. 2014; Johnston et al. 2014; Santoro et al. 2020

What is the influence of the hypoxic water column on iron, manganese and nutrient fluxes in the GoM? Here, collaborators J. McManus (Bigelow Labs) and S. Severmann (Rutgers) and I continue our work on benthic fluxes of iron and manganese from shelf sediments and explore the use of iron isotopes as a tracer of benthic iron recycling. This is still a work in progress but is an extension of work we’ve conducted off the Oregon/California margin.

Papers/Manuscripts related to Gulf of Mexico work:

Berelson et al. 2013; McManus et al. 2012; Homoky et al. 2012; Severmann et al. 2010; Baronas et al. 2016

This is a topic that was recently supported by an NSF award (primarily to L. Yeung, former post-doc in Berelson lab now Asst. Prof. Rice U.). J. Fleming (graduate student) is also in the process (2014) of writing a dissertation on the topic of oxygen uptake rates and their controls. We are examining the variability of these rates, how nutrient addition, changes in pH and temperature impact them and what maximum uptake rates are under glucose additions. Previous work in my lab (Reidel, PhD student) examined oxygen consumption in bacterial cultures under conditions of nutrient stress, in LTSP.

Papers/Manuscripts related to O2 Respiration work:

Riedel et al. 2013; Fleming et al. 2014; Collins et al. 2010