8 April, 2000
LTER Phytoplankton Group; Part 1
Question 49: Has Antarctica always been covered with ice?
This morning, most of Hero Inlet and Arthur Harbor was absolutely packed with brash ice. There was also a very contented-looking Leopard Seal sitting on a growler (small iceberg) that I could see out of my bedroom window. It had the bloody remains of breakfast on the ice next to it. There is so much brash ice that we can't get the boats out, so no diving today.
When I went out with the two LTER boats in March, the phytoplankton group operated the first boat I was with. They took water samples at different depths and measured light intensity (see 3/19 journal entry). The work done by those on Bruiser focused on the rates of primary production, phytoplankton community structure and light absorption properties.
Plankton is the term that refers to the small, living organisms which float in the water. Zooplankton are animal-like organisms, while adding the prefix "phyto" refines the group to include only the aquatic flora or primary producers. These, like plants on land, photosynthesize to produce the energy they need to live. Primary production is the process of creating new material from the sun's energy. The chemical reaction that the phytoplankton carry out, photosynthesis, fixes carbon. All other organisms depend, directly or indirectly, on the energy created by these primary producers. The marine phytoplankton are single-celled organisms that have chlorophyll. They include several species of diatoms, dinoflagellates, and other algal groups. They range in size from 2 um (micrometers) to 20 mm.
Like seasonal land plants, phytoplankton multiply and grow rapidly when conditions are favorable, then numbers decline. These spurts of growth are called blooms. They can be grazed down by zooplankton or dispersed by storms very quickly. How much phytoplankton exists at any given time (biomass) varies with geographic location, depth, season, and plankton size category. Because there is a wide range of size in phytoplankton species, scientists looking at phytoplankton biomass use the concentration of chlorophyll, the green pigment phytoplankton use to produce food from light, to measure it. The coastal and fast ice areas of Antarctica tend to have higher concentrations of chlorophyll than the open water of the Southern Ocean. The Antarctic Convergence is also an area where high chlorophyll concentrations have been found routinely. Phytoplankton can be found deep in the ocean as well as in this phothosynthetic zone. Since they are not fast swimmers, the mixing water layers and currents in Antarctica can move them around. The vertical distribution of phytoplankton is important because the deeper they are in the water, the less light from the surface is available to them. Phytoplankton can't photosynthesize when they reach depths where less than 1% of the ambient surface light is available. In some places with more constant scientific attention, such as McMurdo Station, yearly seasonal blooms have been identified.
Because of the vast area of the Southern Ocean and the extreme nature of its seasonal variations, the phytoplankton biomass and production data that has been taken so far has limitations. More observations, ones that are timed and located based on plankton biology rather than on schedules and scientific workload of research vessels, are needed. Year-round observations, especially in the pack ice zone are lacking due to logistical difficulties. The Palmer LTER observations are from the limited summer period only.
An additional complication is that all phytoplankton data can't be compared. Older studies excluded the smaller sizes of phytoplankton which have now been found to contribute a large percentage of the biomass. The scientific community is working on identifying patterns of phytoplankton biomass and production and the factors that cause them. They need more information about the seasonal progression of primary productivity with latitude, sea state and wind force data. Also, more needs to be known about the physiology of some phytoplankton species, zooplankton grazing rates and rates of loss of phytoplankton cells to sinking and death. These gaps in the data make it difficult to interpret individual observations, identify trends, or make generalizations about the phytoplankton of the Southern Ocean. The Palmer LTER is working to create a solid data set over 10 years in the Palmer area and along their ocean transects that will mesh with existing data.
Answer 48: Antarctica is about 1/10 th of the world's total land surface, about five and one half million square miles. It is the fifth largest continent, about the size of the United States (without Alaska) and Mexico combined. It is mostly covered with ice.
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