Page 102 - University of Pretoria Research Review 2017

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When ‘dark matter’ matters
Thulani Makhalanyane, Centre for Microbial Ecology and Genomics, Department of Biochemistry, Genetics and Microbiology
in shifts in the physicochemical composition of ocean environments. Increased marine water recovery of atmospheric CO2 leads to a reduction in ocean pH, directly affecting the viability of marine ecosystems such as corals, molluscs, and biota echinoderms, fish and algae. In some regions, oceans are also increasing in temperature and becoming more stratified. Increased temperatures directly affect the metabolic rates of organisms and the associated water column stratification restricts the flow of nutrients to the surface. A consequence of oceanic warming appears
to be the expansion and intensification of oxygen minimum zones (OMZs), regions in which oxygen saturation in seawater is at its lowest. This increase in OMZs will have direct effects on the biogeochemical cycling of nitrogen (N), phosphorus (P), iron (Fe) and CO2 in the world’s oceans. The effect of changes in nutrient cycles will directly affect marine biota, although the impacts on microbial communities and the processes they mediate remain unclear.
Previous studies estimate the number of prokaryotic (that is, bacterial and archaeal) cells in the world’s oceans at 1.2 x 1029 (120 000 000 000 000 000 000 000 000 000) with most heterotrophic prokaryotes found in the upper 200m of the open ocean. The identification of these microorganisms has been a significant contemporary challenge, which has resulted in a high proportion of uncharacterised microorganisms with no cultivated
Human activity, including the combustion of fossil fuels, cement production and deforestation, is responsible for about a third of the carbon dioxide (CO2) released into the global atmosphere. As a result of sustained increases in CO emissions over
2
the past 150 years, current atmospheric CO2 levels
are estimated at above 410 ppmV.
Increasing concentrations of carbon dioxide (CO2)
and higher temperatures are significant threats, as identified by the Congress of the Parties (COP) 21 meeting in Paris in November 2015 and supported
by scientists globally. A key resolution at the COP21 meeting was to curb temperature increases to 2°C above pre-industrial levels. Yet, there has been an apparent reluctance to implement the resolutions due to the anticipated short-term negative impact on the economies of highly industrialised nations. Alarmingly, the levels of CO2 emissions are expected to rise for one or more decades, even if the COP21 agreement
is implemented as envisaged. It therefore remains essential to understand the effects of increasing CO2 levels on the Earth’s ecosystems.
A very large proportion of atmospheric CO2 is taken up in the marine carbonate system. In the past two decades, approximately 124 billion metric tonnes of carbon have been absorbed by the oceans, resulting