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Marine Ecology Progress Series

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MEPS 452:45-61 (2012)  -  DOI:

Primary production throughout austral fall, during a time of decreasing daylength in the western Antarctic Peninsula

Maria Vernet1,*, Wendy A. Kozlowski1, Lynn R. Yarmey1,4, Alexander T. Lowe2,5, Robin M. Ross2, Langdon B. Quetin2, Christian H. Fritsen3

1Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, California 92093-0218, USA
2Marine Science Institute, University of California, Santa Barbara, Santa Barbara, California 93106-6150, USA
3Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, Nevada 89512, USA
4Present address: National Snow and Ice Data Center, University of Colorado at Boulder, Boulder, Colorado 80309-0449, USA
5Present address: Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington 98250, USA

ABSTRACT: Antarctic phytoplankton is characterized by a pronounced seasonality in abundance, driven mainly by changes in sunlight. We combined measurements and modeling to describe the influence of changing daylength on fall and winter phytoplankton production in coastal waters of the western Antarctic Peninsula (wAP) in 2001 and 2002. The model was parameterized with field observations from the Palmer Long-Term Ecological program in the wAP during summer and early fall and from the Southern Ocean Global Ecosystems Dynamics program fall and winter cruises to Marguerite Bay and shelf waters. Shorter daylength and a deepening of the mixed layer account for most of the decrease in primary production during March, April, and May. At this time, biomass decreases by an order of magnitude and remains low and constant until the end of August. An additional loss rate was added to the primary production model to fit output to observations. This loss rate, estimated at ~0.1 to 0.15 d−1, is due to physical, chemical, and biological processes such as scavenging by sea ice, zooplankton grazing, cell lysis, and cell sedimentation, which are expected to be high at this time of year. Growth and loss rates of phytoplankton populations are similar on 1 March, with growth decreasing rapidly over time while the loss rates remain constant. By the beginning of winter (1 June), growth is low, with minimum rates in July and increasing towards September. During a period of diminishing food supply, preliminary estimates of grazing indicate that fall biomass could support existing macrozooplankton populations, but the timing and concentration of food supply is variable and expected to affect health of zooplankton as they enter the winter.

KEY WORDS: Phytoplankton · Primary production · Antarctica · Bloom demise · Fall · Winter · Growth rates · Loss rates

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Cite this article as: Vernet M, Kozlowski WA, Yarmey LR, Lowe AT, Ross RM, Quetin LB, Fritsen CH (2012) Primary production throughout austral fall, during a time of decreasing daylength in the western Antarctic Peninsula. Mar Ecol Prog Ser 452:45-61.

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