Occurrence of Nitrogen Fixing Cyanobacterium <i>Trichodesmium</i> under Elevated <i>p</i>CO₂ Conditions in the Western Bay of Bengal

Abstract

Recent studies on the diazotrophic cyanobacterium Trichodesmium showed that increasing CO 2 partial pressure ( p CO 2 ) enhances N 2 fixation and growth. We studied the in situ and satellite-derived environmental parameters within and outside a Trichodesmium bloom in the western coastal Bay of Bengal (BoB) during the spring intermonsoon 2009. Here we show that the single most important nitrogen fixer in today’s ocean, Trichodesmium erythraeum , is strongly abundant in high (≥300 μ atm) p CO 2 concentrations. N : P ratios almost doubled (~10) at high p CO 2 region. This could enhance the productivity of N-limited BoB and increase the biological carbon sequestration. We also report presence of an oxygen minimum zone at Thamnapatnam. Earlier studies have been carried out using lab cultures, showing the increase in growth rate of T. erythraeum under elevated p CO 2 conditions, but to our knowledge, this study is the first to report that in natural environment also T. erythraeum prefers blooming in high p CO 2 concentrations. The observed CO 2 sensitivity of T. erythraeum could thereby provide a strong negative feedback to rising atmospheric CO 2 but would also drive towards phosphorus limitation in a future high CO 2 world.