Testing the Canyon Hypothesis: Evaluating light and nutrient controls of phytoplankton growth in penguin foraging hotspots along the West Antarctic Peninsula Academic Article uri icon

abstract

  • AbstractBiological hotspots along the West Antarctic Peninsula (WAP) are characterized by high phytoplankton productivity and biomass as well as spatially focused penguin foraging activity. While unique physical concentrating processes were identified in one of these hotspots, understanding the mechanisms driving the blooms at these locations is of high importance. Factors posited to explain the blooms include the upwelling of macronutrient and micronutrientenriched modified Upper Circumpolar Deep Water (mUCDW) and the depth of the mixed layer influencing overall light availability for phytoplankton. Using shipboard tracemetal clean incubation experiments in three different coastal biological hotspots spanning a northsouth gradient along the WAP, we tested the Canyon Hypothesis (upwelling) for enhanced phytoplankton growth. Diatoms dominated the Southern region, while the Northern region was characterized by a combination of diatoms and cryptophytes. There was ample concentration of macronutrients at the surface and no phytoplankton growth response was detected with the addition of nutrientenriched mUCDW water or iron solution to surface waters. For all treatments, addition of mUCDW showed no enhancement in phytoplankton growth, suggesting that local upwelling of nutrientenriched deep water in these hotspots was not the main driver of high phytoplankton biomass. Furthermore, the dynamics in the photoprotective pigments were consistent with the light levels used during these incubations showing that phytoplankton are able to photoacclimate rapidly to higher irradiances and that in situ cells are low light adapted. Light availability appears to be the critical variable for the development of hotspot phytoplankton blooms, which in turn supports the highly productive regional food web.

published proceedings

  • LIMNOLOGY AND OCEANOGRAPHY

altmetric score

  • 12.2

author list (cited authors)

  • Carvalho, F., Fitzsimmons, J. N., Couto, N., Waite, N., Gorbunov, M., Kohut, J., ... Schofield, O.

citation count

  • 14

complete list of authors

  • Carvalho, Filipa||Fitzsimmons, Jessica N||Couto, Nicole||Waite, Nicole||Gorbunov, Maxim||Kohut, Josh||Oliver, Matthew J||Sherrell, Robert M||Schofield, Oscar

publication date

  • March 2020

publisher