7. Effects of carbon dioxide on neritic calcifying organisms and carbonate sediments

Calcification rates of several major groups of marine calcifying organisms, from both neritic and pelagic environments, will very likely decrease in response to changes in ocean carbonate chemistry. Although benthic and planktonic calcifiers of both neritic and pelagic communities display a similar response to increased CO₂ forcing, important differences exist between the two that will dictate different approaches toward assessing the larger potential effects of reduced calcification on ecosystem structure and function, how the effects could cascade to other ecosystems, and ultimately, the changes in the ocean carbon cycle.

One of the most significant differences between neritic and pelagic environments in the tropics and subtropics is the volume, mineralogy, and proximity of carbonate sediments on the seafloor within the photic zone. As atmospheric anthropogenic carbon dioxide increases and acidifies the oceans, complex interactions are expected to take place between seawater, calcifying organisms and carbonate sediments. Ultimately how calcifying organisms respond to elevated CO₂ will depend, in part, on these complex relationships. Predictions, based on relatively simple models have been made about the fate of coral reefs and other calcifying organisms. These models forecast as much as a 50 percent loss of coral reef ecosystems by 2100 due to anthropogenic CO₂ . Coral reefs are defined by the geologic structures they build. By some accounts it is only a matter of a few decades before they will become incapable of producing the sediments that form reefs. It is a goal of this research to better understand the complex interactions between sediments, organisms, and seawater chemistry in order to refine portions of these models for more accurate predictions.

This position provides opportunities for interdisciplinary collaboration between many disciplines including chemical and physical oceanography, marine biology and ecology, sedimentology, microbiology, mineralogy, and subsurface (shallow-marine) fluid flow. The postdoctoral fellow would be a member of a team with access to a wide array of marine field and remote sensing capabilities. The team uses geochemical, sedimentological, environmental, ecological, hydrodynamic and image data to develop models or enhance existing models of the carbon chemistry of seawater, circulation, sediment accumulation, coral reef productivity, and ground water. Although numerous aspects of the CO₂ problem are open to investigation, some are less well known than others. Several poorly known aspects are:

1. although many empirical studies have shown that seawater acidification decreases calcification, the mechanisms of calcification and exactly how CO₂ affects them are not known for most calcifying organisms;
2. although there is wide agreement on the solubility of aragonite and calcite, the solubility of biogenic magnesium calcite is not well constrained and yet may control much of the observed dissolution behavior of neritic sediments;
3. current models drive sediment dissolution by bacterial respiration of organic matter and do not take into account dissolution by sulfate reduction/oxidation or dissolution by endolitihic chlorophytes, cyanobacteria, sponges and fungi; and
4. the details of how CO₂ interacts with marine organisms and sediments, the interactions of these processes with other environmental variables such as reef/ocean circulation, nutrients, and temperature are within the realm of this research opportunity if given strong linkage back to reefs, sediments and CO₂.

Proposed Duty Station: St. Petersburg, FL

Areas of Ph.D.: Marine science or similar degree with emphasis in marine science

Qualifications: Applicants must meet one of the following qualifications: Research Chemist, Research Oceanographer, Research Geologist, Research Ecologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Kim Yates, (727) 803-8747, x3059, kyates@usgs.gov; Robert Halley, (727) 803-8747, x3020, rhalley@usgs.gov

Human Resources Office contact: Kathy McDuffie, (703) 648-7408, kmcduffie@usgs.gov

Summary of Opportunities