Description

Ultraviolet radiation influences the dynamics of plankton processes in the near-surface waters of most aquatic ecosystems and, in particular, the Southern Ocean in the austral spring period, when biologically damaging UV-B is enhanced by ozone depletion. Progress has been made in estimating the quantitative impact of UV (and enhanced UVB) in the Southern Ocean for such processes as phytoplankton photosynthesis, bacterial incorporation and DNA damage. 

Our most recent work has focused on the most southerly open water around the Antarctic Continent, the Ross Sea.  Of interest are the spring time blooms of the colonial alga Phaeocystis antarctica, which occurs in a polynya (ice-free region in an otherwise ice-covered ocean) that develops in the southern Ross Sea in October and November. This polynya has particular interest because it results in open water at a far southerly location in the spring, well within the "ozone hole" exposing plankton to elevated UV-B.  The continuous daylight characteristic of this time of year has implications for the regulation of DNA repair, most of which normally occurs at “night.” There are a number of studies suggesting that vertical mixing can significantly modify the impact of UV in the Southern Ocean and elsewhere. However, there are limited measurements of turbulence intensity in the surface layer, and measurements have not been integrated with parallel studies of UV effects on plankton. To better understand how UV affects planktonic processes in the Ross Sea polynya, particularly in the context of vertical mixing, we are modeling vertical motion in the surface mixed layer to generate particle trajectories and the resultant light histories.  Planktonic responses to light are then determined based on the field measurements with natural assemblages conducted during cruises in 2004 through 2006.  The results are enhancing our understanding of vertical mixing processes, trophic interactions and biogeochemical cycling in the Ross Sea.