The Influence of Short-term Events on the Biological and Hydrographic Structure of the Southwestern Ross Sea

Randolph Michael Jones and Walker O Smith Jr, Virginia Institute of Marine Science, Gloucester Point, VA, United States
The seasonal and spatial variations in oceanographic and biological variables in the Ross Sea have been well documented, and interannual variations have also been investigated. However, the influence of short-term events in a small region with relatively little spatial variability – such as storms, passage of eddies, and wind mixing – have received little attention with respect to their role in altering or enhancing the seasonal changes in phytoplankton. We used data from an autonomous glider deployed in the Ross Sea polynya near Ross Island, as well as wind data from a nearby automatic weather station, to investigate the role of these events on phytoplankton dynamics. Two years (2010-2011 and 2012-2013) of data were analyzed. We hypothesized that short-term events significantly altered phytoplankton growth and were associated with enhanced rates of vertical flux, and as a result introduced significant variability into the temporal sequence of phytoplankton blooms. We found significant differences between the two years in all three phases of phytoplankton blooms (biomass accumulation, maxima, dissipation) in the effects that glider- and wind-measured variables (water column properties/structure, mixed layer depth, and wind events) had on phytoplankton biomass. During buildup, wind events increased mixed layer depths and changed water column structure and properties (12-24 h delayed response, dependent on wind intensity and duration), which resulted in short-term interruptions in biomass accumulation in the upper 30 m, but caused vertical flux and biomass accumulation deeper than 50 m. From the maxima through the dissipation period, this delayed response shortened to 2-12 hours leading to substantial vertical flux and biomass accumulation deeper than 30 m. Our results demonstrate that short-term events can significantly introduce changes into seasonal patterns of phytoplankton dynamics and have the potential to impact local biogeochemical cycles.