A Warming World

Li et al., 2009, found a trend in the Arctic Ocean of surface water warming and freshening. Deeper water remained unchanged. As the surface water warmed and freshened, nutrients decreased and the abundance of very small phytoplankton (picoplankton) increased, relative to larger phytoplankton (nanoplankton). The authors proposed that the warming and freshening of the surface waters increased ocean stratification and hence reduced mixing with nutrient-rich deep water. Reduced nutrients favor smaller phytoplankton because they have a higher surface-area-to-mass ratio so they are better able to take up nutrients at low concentrations than larger phytoplankton.

The authors see potential implications for this trend:

1. The picoplankton are so small that they essentially do not settle out of the water column. The least bit of turbulence will keep them in suspension. This reduces the amount of carbon that gets buried in sediments, with implications for the long-term carbon cycle.

2. The picoplankton are more difficult for zooplankton to harvest than larger phytoplankton. This alters the food web.

Launch Model

How would you change the model settings to mimic this change in the Arctic ecosystem? (Type your response in the box below.)

Answer

In an ecosystem with 2 phytoplankton taxa, zooplankton, and detritus:
Phytoplankton 1 (picoplankton): Decrease K for nitrogen because they are better able to take up nutrients at low concentrations.
Phytoplankton 2 (nanoplankton): Increase K for nitrogen because they are less able to take up nutrients at low concentrations.
Zooplankton find it difficult to graze on picoplankton, therefore we make the following changes:

  • Increase K for phytoplankton: picoplankton are more difficult to graze.
  • Increase feed minimum: picoplankton are more difficult to graze.
  • Increase Assimilation: when eaten, less is wasted with picoplankton than with nanoplankton.
  • Decrease grazing maximum: picoplankton are more difficult to graze.

What happens to zooplankton abundance? (Type your response in the box below.)

Answer

In a system described above, zooplankton abundance inevitably decreases. Zooplankton are prey for many other animals including whales, foraging fish, and some sea birds.


Reference: Smallest Algae Thrive As the Arctic Ocean Freshens. Li, W.K.W., McLaughlin, F.A., Lovejoy, C., and Carmack, E.C. (2009): Science, 326, (5952), 539. http://www.sciencemag.org/cgi/content/full/326/5952/539