Introduction

The purpose of this study is to investigate how the marine diatom Thalassiosira weissflogii responds to varying concentrations of carbon dioxide (CO₂).  In particular, this study sought to determine how population growth rate, intracellular photopigment concentrations, and carbonic anhydrase enzyme activity were affected when populations were cultured in 100, 370, and 750 parts-per-million (ppm) CO₂.  Additionally, the culture medium was sampled for available nitrate, phosphate, silicate, and pH so that comparisons could be made between the observed biological parameters and the conditions of the sample media. 

This research seeks to investigate timely questions about the impact of increasing atmospheric CO₂ concentrations on the biosphere.  It has been widely documented that the concentration of atmospheric CO₂ has been steadily increasing since the turn of the 20^th century (Carbon Dioxide Information Analysis Center).  At the present time, atmospheric CO₂ is about 370 ppm, but different models suggest that atmospheric CO₂ concentrations could be 30-150% higher in 2100 (Environmental Protection Agency).  While there is little scientific disagreement over these facts, there is significant controversy concerning the effects that this increase will have on aquatic and terrestrial biomes.

One view focuses on the role of CO₂ as a greenhouse gas (GreenPeace).  Given the effectiveness of CO₂ at trapping heat, proponents of this view warn that increasing concentrations of CO₂ in the troposphere will result in significant increases in global average temperatures.  This, in turn, will likely generate profound changes in global climate that would threaten established agricultural practices in addition to the Earth’s natural flora and fauna.  The other view, however, suggests that increasing levels of atmospheric CO₂ will be beneficial to the environment (Greening Earth Society).  In particular, it is suggested that available CO₂ limits the rate at which photosynthetic organisms can grow, and, with increasing CO_2, the growth of primary producers will increase.  Because of the interdependence of all organisms on primary producers, increasing the biological energy store of primary producers would have large-scale, beneficial impacts on subsequent trophic levels.

In evaluating the merits of these two positions, it is vital that the marine ecosystem be studied.  Oceans account for approximately 66% of the earth’s surface, and it has been estimated that marine algae including diatoms, through CO₂ fixation, are responsible for approximately 40% of the earth’s primary production.  Given the significant rate of photosynthesis in the oceans, this biome is a large and important carbon sink.  Therefore, studying the effects of increased atmospheric CO₂ on marine photosynthetic diatoms seems prudent to understanding the effects of CO₂ on primary production.