Arctic Phytoplankton: Surviving the Winter and Preparing for Spring

Sam Laney, Biology


Arctic Research Initiative
2011 Funded Project


Phytoplankton are the photosynthetic microbes living in the surface ocean that perform the critical ecological role of converting sunlight into biologically useful energy.  Polar phytoplankton living at high latitudes face a basic challenge that their lower latitude counterparts do not, in that phytoplankton at high latitudes experience extended periods of no sunlight each year during winter.  Although polar phytoplankton do not hibernate per se they do adopt special strategies that allow them to survive the dark winter months and yet still be poised to jumpstart photosynthesis and growth with the onset of light in the spring.  Our ecological understanding of how different phytoplankton cope with winter darkness in the Arctic and Antarctic remains very poor.  We know little about which species stay suspended in the water column in wintertime, or how the abundances of these survivors vary spatially in polar seas.  We also have almost no direct observations of the metabolic state of these overwintering species, and thus no basis for predicting which species, if any, will respond first or fastest to the restoration of daylight in spring.  If current trends in Arctic climate continue, the reduction and thinning of seasonal sea ice will dramatically advance the timing when light levels under-ice begin to increase in the spring.  How this will affect the seasonal start of photosynthesis and production in phytoplankton assemblages, as snow and ice cover decrease in spring, remains unclear.

The experiments needed to assess overwintering strategies in polar phytoplankton require ships, yet the few icebreakers capable of conducting meaningful science in polar winter are almost never deployed then.  With WHOI leadership, an unprecedented winter expedition on the US Coast Guard Cutter Healy has now been secured which, when combined with prior ARI-supported advances in examining polar phytoplankton assemblages, presents an unmatched opportunity to assess overwintering phytoplankton in the Arctic.  Proposed here is a plan to use this cruise opportunity to conduct the first -ever broad scale mapping of overwintering phytoplankton distributions in the Bering and Chukchi Seas, utilizing the seagoing Imaging FlowCytobot (IFCB) instrument developed in a federal grant that leveraged prior ARI support.  With this automated approach it is now possible to measure directly the very low numbers of phytoplankton that remain in Arctic waters during winter.  A complementary cell staining technique will be used to discriminate the degree of dormancy in these overwintering populations.  With a platform like Healy it is also possible to conduct the critical grow-out incubations on natural winter phytoplankton assemblages, to determine which species will respond first or fastest to the onset of light in spring.  These three research threads will provide the much needed observations for determining which phytoplankton species are present, alive, and active in Arctic winter, and which ones are best poised to conduct photosynthesis come spring.  Given the uniqueness and scientific originality of this winter Arctic cruise, this proposal also includes real-time outreach efforts to increase the visibility of WHOI Arctic research and leadership in the context of this expedition.