Cindy Lee

We investigated how future ocean conditions, and specifically the interaction between temperature and CO₂, might affect marine aggregate formation and physical properties. Initially, mesocosms filled with coastal seawater were subjected to three different treatments of CO₂ concentration and temperature: (1) 750 ppm CO₂, 16°C, (2) 750 ppm CO₂, 20°C, and (3) 390 ppm CO₂, 16°C. Diatom-dominated phytoplankton blooms were induced in the mesocosms by addition of nutrients. In aggregates produced in roller tanks using seawater taken from the mesocosms during different stages of the bloom, we measured sinking velocity, size, chlorophyll a, particulate organic carbon and nitrogen, and exopolymer particle content; excess density and mass were calculated from the sinking velocity and size of the aggregates. As has been seen in previous experiments, no discernable differences in overall nutrient uptake, chlorophyll-a concentration, or exopolymer particle concentrations could be related to the acidification treatment in the mesocosms. In addition, in the aggregates formed during the roller tank experiments (RTEs), we observed no statistically significant differences in chemical composition among the treatments during Pre-Bloom, Bloom, and Post-Bloom periods. However, physical characteristics were different and showed a synergistic effect of warmer temperature and higher CO₂ during the Pre-Bloom period; at this time, temperature had a larger effect than CO₂ on aggregate sinking velocity. In RTEs with warmer and acidified treatment (future conditions), aggregates were larger, heavier, and settled faster than aggregates formed at present-day or only acidified conditions. During the Post-Bloom, however, aggregates formed under present and future conditions had similar physical properties. In acidified tanks at ambient temperature, aggregates were slower, smaller and less dense than those formed at the same temperature but under present CO₂ or under warmer and acidified conditions. Thus, the sinking velocity of aggregates formed in acidified tanks at ambient temperature was slower than the other two cases. Our findings point out the potential of ocean acidification and warming to modify physical properties of sinking aggregates but also emphasize the need of future experiments investigating multiple environmental stressors to clarify the importance of each factor.

This is a personal account of some of the people and factors that were important in my career in chemical oceanography. I also discuss two areas of oceanographic research and training that I think need more attention. The first is how the difficulty in getting appropriate samples hampers our ability to fully understand biogeochemical processes in the sea. I have worked on dissolved materials, suspended and sinking particles, and sediments in lakes, oceans, rivers, and aerosols. Sample collection problems affect all those areas, although to different degrees. Second, I discuss a few of the issues that I most worry about with regard to graduate education in oceanography, among them an apparent decrease over the past several decades in the ability of many beginning students to write clearly and think logically.

Coomassie stainable particles (CSP) are protein‐containing transparent particles that can be stained with Coomassie brilliant blue (CBB) and are found abundantly in aquatic systems; however, their distribution and role remain poorly known, in part due to the lack of an efficient method to study them. We developed a new, simple, and low cost semi‐quantitative spectrophotometric method for determination of CSP in aquatic systems. The method is analogous to that used to quantify polysaccharide‐rich gel particles called transparent exopolymeric particles (TEP). CSP concentration is determined relative to bovine serum albumin (BSA) standard aggregates (in a manner similar to how TEP is quantified relative to xanthan gum). The method is based on the linear relationship between CSP concentration and the absorbance of the eluted dye from a CBB‐protein complex, which has an absorbance maximum (λmax) at 615 nm. The limit of detection and the precision (%RSD) for the proposed method are 6 µg BSA equivalent and 11%, respectively. The new spectrophotometric method was validated with the existing microscopic method. This new method to quantify CSP is simple, enables rapid measurements, and allows a more efficient comparison with TEP concentrations than the present microscopic method. The spectrophotometric analyses will further the investigation of the abundance, distribution, and role of CSP in the biogeochemistry of the ocean.