CaCO3 Dissolution Kinetics

This Ocean Acidification study (NSF funded) is a collaborative project with J. Adkins (Caltech)—our objective is to use novel geochemical approaches and new devices to examine carbonate dissolution kinetics. 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 that occurs 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 Ksp. We also plan to conduct dissolution experiments in the ocean using a novel Niskin incubator device. This project is in progress with A. Subhas (grad student, Caltech) leading the lab work and manuscript preparation.


ETSP N Fluxes

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


ANACONDAS Amazon Plume Study

ANACONDAS was a large group project led by T. Yager (U. Georgia) aimed at understanding the role that the Amazon Plume plays and played in modifying ocean ecology and C fluxes in the NW Atlantic Ocean. Several cruises between Barbados and the Amazon River mouth provided the opportunity to deploy floating sediment traps, determine oxygen triple isotopes, and collect over 40 sediment cores. The coring effort (lead by graduate student L. Chong) aimed to define the extent of biogenic sedimentation under the plume region and examine Glacial and Holocene sedimentation patterns in this broad region.


Papers/Manuscripts related to ANACONDAS work:

Yeung et al. 2012; Chong et al. 2013; Goes et al. 2014


Gulf of Mexico Benthic Fluxes

What is the influence of the hypoxic water column on iron, manganese and nutrient fluxes in the GoM? Here, collaborators J. McManus (U. Akron) 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.

Benthic Fluxes

Papers/Manuscripts related to Gulf of Mexico work:

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


Laminated Sediments and N Isotopes

The relationship between N cycling in oxygen minimum zones and in anoxic sediments has been a subject our group has been studying for a long time. We take a keen interest in the microbial transformations involving N uptake, production and transport in sediments underlying OMZs and in the potential to translate N isotope patterns into an understanding of OMZ behavior in the past. C. Tems (graduate student) is presently (2014) working on N paleoproxies in laminated sediments off Mexico and California.

Laminated Sediments

Papers/Manuscripts related to N work:

Tems et al. 2014; Deutsch et al. 2014; Townsend-Small et al. 2014; Prokopenko et al. 2013; Chong et al. 2012; Prokopenko et al. 2011; Prokopenko et al. 2006


Oxygen Respiration in the OMZ

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

Microbial Growth Rates

For the past several years, H. Johnson (CSUF) and I have worked with students in the International Geobiology Summer Course investigating the growth rate of microbial mat layers under conditions of +/- light and various trace element additions. These efforts have led to various published abstracts but no publications. Anyone out there interested in taking on this project?